This invention relates generally to the rotor windings of a dynamoelectric machine, and more particularly, to means for ventilating the end turn conductors of the windings.
For uniformity and ease of understanding, the following terms when used in this specification and claims, have the meaning specified. It is to be understood that the technical literature does not necessarily always agree, nor is it always internally consistent. A conductor, the element which conducts electricity, typically comprises copper and forms the other members of the current carrying path. A turn is one electrical loop around a pole of a rotor. A coil comprises all turns that are disposed in a predetermined axially extending slot, or coil slot, in the circumference of the rotor. A winding comprises all concentric coils in the rotor.
A rotor of a gas cooled dynamoelectric machine includes a central rotor body portion defining a plurality of axially extending coil slots within which are disposed a plurality of coils. The slots are circumferentially spaced on the periphery of the rotor body on either side of a pole portion of the body such that all coils disposed about the same pole portion are typically concentric and form a winding of the rotor.
In order to generate an electromagnetic field for the dynamoelectric machine, a respective plurality of conductors constituting the winding carries current in loops about each pole of the rotor. The conductors axially extend and are radially stacked in the coil slots to form turns with layers of insulation interposed between each turn. When current is flowing in the conductors, heat is generated by I.sup.2 R losses in the conductors. Rotor windings with non-uniform temperature profiles experience higher levels of thermal distortion and vibration, due in part to increased thermal expansion, and consequently a lower level of reliability than rotor windings with uniform temperature distributions.
Many cooling schemes for directly cooling rotor windings use coolant gas flow through a path in a longitudinal duct of a conductor. However, since coolant gas that flows in a longitudinal duct in a conductor experiences an increase in temperature as it picks up heat along the length of the duct, rotor windings with long coolant ducts produce large temperature rises in the coolant gas and associated conductor. The longer the cooling duct is, without provision of supplemental cooling, the greater is the hot spot temperature, i.e. maximum absolute temperature, and the higher is the average temperature of the coil. Local hot spots are sometimes minimized by situating a second duct in each turn in the vicinity of the hot spot. However, on some rotor winding designs the conductors forming the turns are too narrow to accommodate two grooves in the same turn.
In one known cooling scheme, coolant gas enters a single channel near the pole centerline and flows through the turn corner and axially toward the rotor body. The flow in a radially outer and in an adjacent radially inner turn join into a single channel disposed in the radial outer of the two turns. Gas from the radially inner turn joins the flow of gas in the radially outer turn through a hole in the copper coil and turn insulation located just outboard the axial end of the rotor body. A fresh supply of coolant gas is then introduced into the radially inner turn just inboard the location at which the two outboard gas flows are combined.
Another scheme involves separate internal passages disposed in the axially lying portions of the coil and the circumferential end portions of the coil, respectively. Gas flowing in the circumferential end portion is kept separate from gas in the axially lying conductors by an elaborate and expensive baffling scheme. Coolant gas may be discharged through the centering ring or pole face of the dynamoelectric machine. Baffling is also required for winding coolant systems that have a gas inlet and gas outlet disposed relatively close to each other in order to maintain adequate gas pressure differential for urging coolant gas flow through internal passageways in the conductors.
Accordingly, it is an object of the present invention to provide cooling of the rotor winding of a dynamoelectric machine wherein the rotor winding includes narrow turns which will not accommodate two adjacently disposed gas passages.
Another object of the present invention is to maintain a substantially uniform temperature profile in the end turn of a rotor winding.
Yet another object of the present invention is to eliminate the need for baffling, such as is required in ventilation schemes that discharge coolant gas through the centering ring or the pole face of a dynamoelectric machine.